How to edit normal direction
If you need all the normals to point upwards it's quite simple.


Create a new plane.
Enable Auto-Smooth on your main object.





Add a Data Transfer Modifier to your main object.
Set the Plane as source Object and check Face Corner Data and enable
Custom Normals. Your object will now copy the normals from the Plane.






If you want different normals to point in different directions you can do the same using Vertex Groups.


Create a new plane and angle it to the direction you want your normals to point. Create a new plane for every direction you need. Name them accordingly.





Create a Vertex group for each direction. Name them accordingly. Assign the vertices  you need to their desired vertex group.





Enable Auto-Smooth
Add a Data Transfer Modifier for each Vertex group. Set the desired Plane as source Object along with its Vertex group. Check Face Corner Data and enable Custom Normals.